Selective protective system for more than two parallel feeders



R. VULZING Feb. 24, 1931.

SELECTIVE PROTECTIVE SYSTEM FOR MORE THAN TWO PARALLEL FEEDERS Filed Dec. 2, 1926 Array v5) Patented Feb. 24, 1931 ATENT OFFECE RUDOLE VCLZING, OF BERLIN-SIEMENSSTADT, GERMANY, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF FENNSYL- VANIA SELECTIVE PROTECTIVE SYSTEZVT FOR MORE THAN TWO PARALLEL FEEDERS Application filed December 2, 1926, Serial No. 152,235, and in Germany December 4, 1925.

My invention relates to a selective protective system for more than twoparallel feeders.

There are already known systems for the selective or discriminative isolation of defective feeder for any number of parallel feeders, in which directional relays are connected between the center and the corner points of a polygon formed by the secondaries of current transformers placed in the individual feeders to be protected.

My invention consists of a system or means for supplying to such directional relays connected in the known manner, the voltage without employing special voltage transformers.

Vith this end in view, according to my invention, bifilar choke coils or reactors are placed between any two transformers in such a manner that their centers form the corner points of the polygon with which are connected the current coils of the directional relays. The voltage coils of each directional relay are connected with the two. ends of the corresponding choke coils.

In the drawing afiiXed hereto:

Fig. 1 is a schematic showing of my invention as applied to three parallel feeders, one phase only of which is shown,

Fi 2 is a schematic showing of a system for ensuring the response of the protective means of the remaining feeders after a defective feeder has been isolated, and

Fig. 3 is a schematic showing of a system for ensuring the response of the protective means in the event of a ground.

Referring to Fig. 1 of the drawing a, Z), 0 are the feeders to be protected and 11, 12, 13 the current transformers. Between the secondaries of said current transformers are connected the bifilar choke coils or reactors 14, 15 and 16. The effect of the biiilar choke coils may be improved by the loading resistors 80, 31 and 32. The directional relays d, e and f are of the usual watt-meter type employing current windings 17, 18 and 19, and voltage windings 20, 21 and 22, respectively, to control the operation of contacts in accordance with the magnitude and direction of the energization thereof.

Under normal circuit conditions, the magnitudes of the currents traversing the two windings of the bifilar coils 14, 15, 16 are equal and opposed so that the voltage windings 20, 21 and 22 are not energized. Upon the occurrence of a fault however, such as indicates at 23 in the feeder b, the energization of the two windings of the coil 15 is altered with respect to each other, and a potential difference occurs across the coil which energizes the voltage winding 21 of relay 0. The directional relay 0 then becomes operative and closes the tripping circuit through the solenoid 28, which attracts its plunger and opens the switch 25 in the feeder b.

In order to ensure the correct response of the protective means or system for the remaining feeders, subsequent to the isolation of a defective feeder, it is necessary that the parts of the protective means related to the defective feeder be disconnected or shortcircuited. It is therfore in the case under consideration necessary to bridge the secondary of the current transformer 12 and the bifilar choke coil 15 by a short circuit connection and also to break the connection between the neutral point of the bifilar choke coil 15 and the current coil 18 of the relay 6.

This may be effected by providing each of the switches 24, 25 and 26 with a contact member which in the closed position of the switch bridges two contacts placed in the connection of the respective bifilar choke coil to the correpsonding current coil of the relay,

and which when the switch is opened bridges two contacts, one of which is connected with the beginning of the secondary of the corresponding current transformer and the other with the end of the corresponding bifilar choke coil or reactor.

Such an arrangement is illustrated in Fig. 2 of the drawing.

Referring to this figure, 25 is the switch operatively connected in the feeder b. the

movable part of which is provided with the T contact member 3%. This contact member closes the pair of contacts when the switch is opened. One of said contacts connected with the terminal at the begining of the secondary of the current transformer 12 in the feeder b and the other of said contacts is connect-ed with the terminal at the end of the bifilar choke coil belonging to the relay 6, which controls the switch 25. hen the switch is closed the contact member bridges the two contacts 36, placed in the connection between the neutral point of the biiilar choke coil 15 and the coil 18 of the relay 6. I

. In order to make sure that the protective system also responds correctly in case of a ground, current transformers must be placed in all phase conductors of a feeder. lfthe system should become operative only in the case of a short circuit between any two conductors, the'current transformer in one condoctor of a complete polyphaseline may be omitted. In a three-phase system two trans formers will therefore suffice for each threephase feeder. The two transformers of two phases may then in known manner be connected in opposition, diagrammatically illustrated in Fig. 3 of the or wing. ln this way a substantially simpler arrangement of the circuits is obtained. In this figure 4:1, 42 and 43 are the three-phase busbars and 44, 45, 46, and 47, 48, 6 .9 and 50, 51, 52 the three outgoing parallel three-phase feeders. In two phasesof each of these feeders viz, in 4A and L5, as well as 4:? and 48 and likewise 50 and 51 are placed current transformers. The two secondaries of these current transformers are connected in opposition and these groups are connected in series across the bifilar choke coils 53, 54 and 55. With the neutral points of these three bifilar choke coils or reactors are connected the current coils of the threerelays 56, 57 and 58 and the second coils of placed thereon as are imposed by the prior art.

I claim as my invention 1. In a protective system, the combination with a plurality of parallel feeders, current transformers operatively associated with said feeders, a bifilar choke coil connected in circuit with the secondary windings of said transformers, and means for effecting the disconnection of a feeder in response to a fault therein including a power-directional relay having a current and a voltage winding, means for energizing said current winding in accordance with the current traversing said transformers, and means for energizing said voltage win-ding in accordance with the of connected to the midpoint of said choke coil and the other terminals connected to each other, and said voltage windings connected across the terminals of said choke coil.

In a protective system, the combination with plurality of parallel feeders, current transformers operatively associated therewith, a loop circuit including the secondaries of said transformers, bifilar choke coils con nected in series in said circuit, and neans for effecting he disconnection of a feederin responseto the occurrence of a fault therein comprising power-directional relays having current and voltage windings, said current windings having one of the terminals thereof connected to the midpoint of said choke coil and the other terminals connected to each other, and said voltage windings connected across the terminals of said choke coil, and means operative upon the disconnection of a defective feeder for rendering ineffective the transformer secondary and hifilar choke coil associated therewith. f

In testimony whereof, I have hereunto subscribed my name this 15th day of November,

RUDOLF VOLZI-NG. 

